Sprinkler irrigation systems

ABSTRACT

This specification discloses a sprinkler irrigation system comprising a sprayline swivelly secured to a central water hydrant, a plurality of hydraulic towing devices connected to said sprayline and driven by the water therein, said towing devices being interconnected by a tie line swivelly secured to the hydrant and constraining the towing devices to more in a circular path. The outermost towing device controls the rate of movement of the whole system through control means connected to each intermediate towing device and operated by changes in the angular position of the tie line relative to the intermediate towing device.

United States Patent 1,

de Laine et al.

SPRINKLER IRRIGATION SYSTEMS Filed: Apr. 21, 1971 App]. No.: 135,863

Foreign Application Priority Data Apr. 22, 1970 Australia ..0982/70 Dec.21, 1970 Australia ..3551/70 US. Cl. ..137/344, 239/212 Int. Cl .1..B05b 9/02, EOlh 3/02 Field of Search ..239/190, 191, 272,

References Cited UNITED STATES PATENTS 9/1957 Clayton ..239/191 X 51 May1, 1973 2,893,643 7/1959 Gordon 137/344 2,941,727 6/1960 Zybach..239/212 X 3,259,319 7/1966 Wal1ace.. ..239/212 X 3,500,856 3/1970Boone et a1. 137/344 3,605,928 9/1971 Loesch 3,610,531 10/1971 EI'lCkSOn..239/191 FOREIGN PATENTS OR APPLICATIONS 734,313 5/1966 Canada..239/191 Primary Examiner-Samuel Scott Att0rneyCushman, Darby & Cushman[57] ABSTRACT This specification discloses a sprinkler irrigation systemcomprising a sprayline swivelly secured to a central water hydrant, aplurality of hydraulic towing devices connected to said sprayline anddriven by the water therein, said towing devices being interconnected bya tie line swivelly secured to the hydrant and constraining the towingdevices to more in a circular path. The outermost towing device controlsthe rate of movement of the whole system through control means connectedto each intermediate towing device and operated by changes in theangular position of the tie line relative to the intermediate towingdevice.

12 Claims, 15 Drawing Figures Patented May 1, 1973 3,730,211

5 Sheets-Sheet 1 Patented Mly 1, 1973 5 Sheets-Sheet J Patepted May 1,1973 3,730,211

5 Sheats Sheet 4 Patented May 1, 1973 3,730,211

5 Sheets-Sheet 5 SPRINKLER IRRIGATION SYSTEMS This invention relates tosprinkler irrigation systems for pastures and the like, and moreparticularly to an improved system having means for continuouslychanging the location of the sprinkler line in a predetermined area tobe watered.

While several different sprinkler irrigation systems are presentlyavailable, each system suffers from certain disadvantages, either interms of the capital cost of the system or in terms of the laborrequired to shift the system from one location to the next. The knownsystems fall broadly into four categories.

The first type comprises a series of pipes joined together withcouplings to form a spray line. Sprinklers of one type or another aremounted at intervals usually thirty feet apart along the sprayline. Inuse, this system has the disadvantage that after watering one area, theline must be drained, manually disassembled and the components moved andreassembled at the next area. This system of sprinkler irrigation issuitable for small areas only, as the labor involved in shifting thesprayline is too costly and too inconvenient for larger acreages.

The second type of sprinkler system uses pipes and sprinklers similar tothe first but the sprayline is mounted on skids or on dual castoringwheels which allow the drained line to be disconnected from its supplypoint and towed by tractor to the next area to be watered. However,since the spray line is generally required to be located 60 feet awayfrom and parallel to the initial position there may be difficulties inmoving the line into such a position by towing from one end.

An alternative to the end two system is the side roll system where up toten chains of sprayline may be rolled sideways by one man with thesprayline mounted on wheels each of whose axis of rotation is thesprayline itself. Whilst this method is easier to operate than the handmoved or end towed methods, it is more expensive and still involvesuncoupling and recoupling the supply end of the sprayline to hydrants.

The third type of system is a sprayline supported four to six feet abovethe ground on Wheeled or tracked supportingunits at sixty to eighty feetintervals. The supply end of the sprayline is connected to a swivelhydrant supplied with water from an underground main. The entireradially disposed sprayline is power moved in a circular path around thecentral hydrant by means of water cylinders and pistons or electricmotors, located on each of the supporting units. The sprayline may be upto six hundred feet in length to cover a circular area of approximately30 acres. The cost of this automatic system is very high and is tooexpensive a system for pasture irrigation.

The fourth type of sprinkler system is a fixed or permanent system ofunderground pipes with sprinklers attached by vertical'risers. Whilstthis system requires minimum labor to operate, the cost of the materialsis very high and this limits its application to valuable cash crops.

A further disadvantage with presently known sprinkler irrigation systemsis that the area to be watered usually has to be surveyed and eachinstallation custom designed by the manufacturer to achieve optimumresults with minimum capital expenditure. This work and the resultingoverheads add to the cost of sprinkler irrigation systems. If the surveyand individual design could be reduced to a minimum, this would in turnlower the cost of sprinkler irrigation systems.

It is therefore an object of the present invention to provide asprinkler irrigation system which, at least to a certain extent,overcomes the disadvantages of the known systems described above.

The invention provides in one aspect an irrigation system comprising anelongate sprayline adapted for connection at one end to a source ofwater under pres sure, an hydraulic towing device connected to the otherend of said sprayline, said towing device comprising a cylinder housinga piston having a piston rod which extends from said cylinder, valvemeans operable to cause said water under pressure to reciprocate saidpiston and piston rod relative to said cylinder, supporting means forsaid piston rod, said cylinder and supporting means each including aone-way essentially preventing movement of said cylinder and said pistonrod in one 7 and the same direction so that the towing device moves in aforward direction only.

In another aspect, the invention provides an irrigation systemcomprising an elongate sprayline or other water line adapted to beswivelly connected at one end to a source of water under pressure, atowing device connected to the other end of said line, said towingdevice being constrained to move in a substantially circular path bymeans of a tie line connected to said towing device and swivellyconnected at the center of said circular path.

In either of the above aspects of the invention, there may be one ormore similar towing devices arranged intermediate said towing device andthe source of water, said sprayline extending between said devices andpreferably tailing behind the devices in loops or bows extending betweenthe devices.

The invention will now be more particularly described with reference toa preferred embodiment shown in the accompanying drawings. It is to beunderstood that while the embodiment relates to a system irrigating acircular area, the towing devices may be adapted to follow other paths.

FIG. 1 is a plan view of a sprinkler irrigation system embodying theinvention;

FIG. 2 is an enlarged plan view of the swivel connection of the systemof FIG. 1;

FIG. 3 is a sectional side, elevation taken along line 33 of FIG. 2;

FIG. 4 is a plan view of outermost towing deviceused in the system;

FIG. 5 is a side elevation of the towing device;

FIGS. 6 and 7 are sectional end elevations taken along lines 6-6 and7-7'respectively of FIG. 5;

FIG. 8 is a fragmentary sectional side elevation of the cylinder of thetowing device showing the piston in the cylinder moving forwardlycondition;

FIGS. 9 and 10 are schematic diagrams showing the opening and closingaction of the valve in the piston;

FIGS. 11 and 12 are fragmentary plan views of intermediate towingdevices showing two alternative forms of control mechanisms;

FIG. 13 is a fragmentary plan view of the rear end of an intermediatetowing device showing the attachment of the sprayline thereto;

FIG. 14 is a perspective view of a sprinkler on a sprayline, and

FIG. 15 is a perspective view of one means of supporting the tie wire ofthe system.

Referring firstly to FIGS. 1 to 3, the system embodying the inventionincludes a sprayline I connected at its innermost end to a rigid pipe 2which is in turn connected, through a suitable flexible connector 3, toa swivel connection of a hydrant 4 located at the center ofa circulararea A to be watered.

The outer end of sprayline 1 is connected to an hydraulic towing device5 and the intermediate portions of the line are connected to two similartowing devices 6 and 7 so that the sprayline 1 extends between the pipe2 and the three towing devices in three approximately semi-circulartrailing loops. Each sprayline loop has a plurality of spaced sprinklerunits 8, such as that shown in FIG. 14.

The three towing devices 5, 6 and 7 are interconnected by a tie wire 9,looped at its inner end to engage the hydrant 4 and fixed to each of thetowing devices. The tie wire 9 is maintained in tension by the towingdevices 5, 6 and 7 and its function is to constrain the latter to movein circular paths about the swivel axis of the hydrant 4. It is believedthat the towing device 5 will probably naturally maintain a circularpath. However, if this is proved incorrect, the device 5 may have itsnose skewed slightly outwardly of the circular path by a further tiewire extending from the wire 9 to the rear end of the towing device topull this end inwardly of the circle or in some other suitable manner.

To prevent the radial force applied to pipe 2 by the dragging ofsprayline 1 damaging the swivel joint, the hydrant 4 is surrounded by aring 10 fixed to the ground by spikes as shown and the inner edge of thering is engaged by a wheel 11, the vertical axle of which is rigidlyfixed to the pipe 2. The pipe 2 is also supported above the ground bywheel or wheels 13, the flexible connector 3 allowing some movement ofthe pipe 2 due to irregularities in the ground surrounding the hydrant4.

The three towing devices 5, 6 and 7, are substantially identical inconstruction so the outermost device 5 will now be described withreference to FIGS. 4 to 7. The towing device 5 comprises a cylindermounted on two tubular skids 16, in the manner shown in FIGS. 6, theskids 16 having a forwardly inclined nose member 17 attached thereto toprevent the skids l6jamming on irregularities in the surface of theground.

The cylinder 16 houses a piston 17 having a suitable seal (not shown) inits periphery and having a tubular piston rod 18 rigidly secured theretowhich extends through an end plate 19 sealingly secured to the cylinderand supporting a suitable seal (FIG. 8) for the rod 18. A skid assembly20 comprising a sleeve 21, two skids 22 connected to the sleeve 21 asshown and an inclined nose member 23 attached to the forward end ofskids 22 is secured to the piston rod 18 by means of clamping bands 24surrounding the sleeve 21. The end of rod 18 is closed except for aninlet fitting 25 for the connection of sprayline 1. The sprayline isalso connected to the sleeve 21 by towing line T to prevent draggingforces being applied to fitting 25.

The skids 16 and 22 for the cylinder 15 and pistons rod 18 each supporta plurality of one-way devices which essentially prevent rearwardmovement of both the cylinder 15 and piston rod skid assembly 20. In thepresent embodiment, each one-way device comprises a pair of trailinglegs 26 interconnected by a rod 26a which passes through suitable holesor bearings in the skids and a sleeve 26b located between the skids.Each rod 26a extends transversely of the longitudinal axis of thecylinder 15 and piston rod 18 so that the legs 26 are free to pivotabout the axis of the rod 26a. The trailing leg 26 has a bent endportion 27 which prevents the leg digging too far into the ground.Alternatively, a plate, stop or other depth control means is provided.It will be clear that any rearward force applied to either of the skidswill cause a small amount of rearward movement until the legs 26 diginto the ground to resist such a force. Thus the legs 26 essentiallyprevent rearward movement of both skids and therefore the cylinder andpiston rod.

Referring now to FIG. 8, it will be seen that the cylinder 15 is closedat its forward end by an end plate 28, similar to end plate 19, the twoend plates being sealingly held in engagement with flanges on thecylinder by the bolts 29. A water discharge pipe 31 is secured in athreaded aperture in the plate 28. The pipe 31 is interrupted by acontrol valve 32 and terminates in a sprinkler head 33 so that the waterdischarged from the cylinder is utilized.

The piston 17 is formed with a water passage 34 and a valve assembly Vis supported by the piston 17 as shown in FIG. 8. The valve assembly Vcomprises a valve stem 35 slidably mounted in a support 36 comprisingtwo opposed rods passing through and fixed to piston 17 and platesthrough which the stem 35 passes. The stem at the forward side of thevalve is surrounded by a sleeve 35a, the purpose of which will beexplained. A valve 37 is slidably mounted on stem 35 and a tensionspring 38 is secured thereto and to a washer 39 fixed to the stem. Ashroud 40 which houses the valve 37 when open is secured to one of theplates of the support 36. The piston rod 18 is also formed with a waterpassage 37 for the delivery of water into the cylinder 15.

The operation of the towing device will be described with reference toFIGS. 8 and 9. In FIG. 8, the piston 17 is shown near the forward end ofits stroke with the stem 35 about to engage end plate 28. Referring nowto FIG. 9(a), the piston is at the forward end of its stroke with thestem 35 pushed to the right and the spring 38 extended and storingenergy. At this time the sleeve 35a engages the valve to lift itslightly from its seat whereupon the spring 38 retracts the valve 37rapidly into its shroud 40 (FIG. 9(b)) where it is protected from theinfluence of the water movement through passage 34. The length of stem35 and sleeve 35a and the rating of spring 38 are selected so that atthe time the valve 37 is first lifted from its seat, the force stored inspring 38 just exceeds the force of the water on the valve 37.

When the valve 37 is unseated, both sides of the piston are exposed tothe same water pressure. However, since the area of the front face ofpiston 17 is far greater than that of the rear face, the water pressure.will attempt to force the piston rearwardly. However, the one-waydevices 26 on the piston rod skid assembly 20 dig into the ground andprevent any such movement i so the cylinder 15 is forced forwardly. Eventhough the valve 32 is always open in the case of device 5 andintermittently open in the case of devices 6 and 7 and water dischargedtherefrom, the difference in areas of the piston faces is sufficient toovercome this. In addition the opening 34 is smaller than the opening inend plate 28.

At the other end of the piston stroke the stem 35 en gages end plate 19to move the valve towards the closed position (FIG. (a)). The valve 37is closed on further movement of the stem. The piston is then pushedforwardly in the cylinder which is held against rearward movement by theone-way devices 26 on the cylinder skids 16. Water is expelled throughthe pipe 31 so valve 32 controls the rate of forward movement of thepiston 17 and thus the rate of movement of the towing device.

As mentioned above, the towing devices 5, 6 and 7 are interconnected bytie wire 9. Unless this tie wire is maintained approximately straight,the towing devices would not remain at their required distances from thehydrant and it is therefore necessary to make suitable provision toensure that the towing devices remain approximately in line.

For this purpose, it is necessary for the average linear speeds of thedevices to be proportional to their distances from the hydrant 4 so thatif they have a common cycle time or frequency of operation, the lengthof the stroke of each piston could be adjusted so as to be proportionalto the radial distance of the respective unit from the hydrant. Whilethis would not ensure that the units remained in line, it would ensurethat substantial misalignment would require an appreciable time.

In addition however, control devices are provided to limit the extent towhich any intermediate towing device may move ahead of the tie line 9connecting the hydrant to the outermost towing device and this isachieved by causing the resultant change in the angular positions of thedifferent sections of the tie wire 9 to adjust a discharge valve at theforward ends of the cylinders to cause either a decrease or an increasein the speed of movement of the respective pistons.

The controller of FIG. 1 1 comprises a valve actuator 43 secured to thespindle of a 90 control valve 32'. The actuator 43 has its free end incontact with a control wire 44, say through an eyelet at the end ofactuator 43, the control wire is secured to tie wire 9, which in thisarrangement is secured near the rear end of cylinder 15, and issupported by pulleys 45 suitably mounted on the cylinder 15. A torsionspring 46 is fixed between actuator 43 and the valve body and biases theactuator to the open position of the valve 32. Thus if the towing devicefalls behind the towing device 5, the change in position of the sectionsof the wire 9 on either side of the cylinder causes a slackening ofcontrol wire 44 and the spring 46 moves the actuator 43 to partly orfully open valve 32' to start that device moving or increase its rate ofmovement. Then when the device starts to overtake device 5, control wire44 is drawn taut to move actuator 43 to partly or completely closethe.valve to slow or stop the towing device.

In the embodiment of FIG. 12, the tie wire 9 is con nected directly totwo arms 47, 48 each pivoted to the cylinder 15. Arm 47 extends wellbeyond its pivot nd has one end of a control wire 49 secured near itsend. This wire 49 passes over a pulley 50 on arm 48 and pulley 51 on thepivot of both arms to a valve actuator 53 which is biassed towards theopening direction by spring means 54. The operation of this embodimentwill be obvious from the drawing and the device functions in anidentical manner to the embodiment of FIG. 11 to control the rate ofmovement of an intermediate towing device.

FIG. 13 shows one suitable way of connecting the sprayline 1 to thepiston rods of the intermediate towing devices 6 or 7. The two sectionsof sprayline 1, connected by a length of flexible tubing 58 of similardiameter to the sprayline pipe, are secured to the skids 22 or thesleeve 23 by meansof chains 56 connected at one end to an eyelet or hook57 and at the other end to a clamp 55 securing the sections of spraylinel to tubing 58. This form of connection allows universal movement of thesections of line 1 relative to the towing device. A smaller diameterhose 59 connects the tubing 58 to the inlet fitting 25 on the piston rod18.

In connecting of the sprayline 1 to the outer towing device 5 asdescribed the dragging forces applied by the plied tothe piston rod 18which therefore would tend to bind and produce excessive wear in theseals of the piston and rod. This lateral bending moment may be resistedby a furrow wheel (not shown) secured to the skid assembly 20 andarranged behind towing device 5. This furrow wheel would be arranged soas to tend to pull the piston rod outwardly and thus counteract theinward pull of the sprayline 1.

The application of lateral forces to the cylinders 15 and the consequentreduction in the tension in tie wire 9 is resisted by the provision of aknife edge runner K secured to the cylinder skid 16 parallel thereto andextending slightly below the lower most point of the skid. The knifeedge may be secured to the cylinder or may be replaced by a disc orother means.

To maintain the sprinklers 8 in an upright condition, a dished skid 60may be fitted to the sprayline l or sprinkler 8 as shown in FIG. 14.

FIG. 15 shows a suitable support wheel 61 for tie wire 9 in systemswhere the distance between towing units is large.

The cylinders, piston rod, piston and skids are preferably formed fromsuitable plastics materials such as p.v.c. although other suitablematerials may be used.

The sprayline is preferably formed of high density polyethylene hoseslightly smaller in diameter than the piston rod, although suitablemetal pipes provided with joints to allow theloops shown in FIG. 1 to beformed may be suitable. For irrigation of smaller areas smaller pipe(s)may be used and only one towing device may be required. Similarly, whilethe cylinder and piston rod are shown to be skid mounted, they may besup- .ported by wheeled structures inwhich case the oneway device may bein the form ofrachet devices fitted to the wheels. Alternatively, thecylinder may engage the ground directly or be mounted on a flat skid inwhich case the one-way devices may be secured to the cylinder bysuitable mounting members.

While in the preferred embodiment the piston control valve is mounted inthe piston, another form of valve may be mounted externally of or formedintegrally with the cylinder to achieve the necessary application ofwater pressure to opposite sides of the piston.

It will also be appreciated that the invention may be applicable toirrigation of playing fields or domestic lawns. For such areas, orsmaller pastures, one towing device may suffice. Similarly the towingdevice may be in the form of a childs toy driven by the household watersupply and the word sprayline as used in the appended claims should beunderstood to include domestic hoses.

As an alternative to the ring 10 and wheel 11 arrangement, the hydrantmay simply be suitably braced against the radial force.

To reduce the tensile forces applied to the piston rod, a tie rod undertension may be secured between the piston 17 and the closed end of thepiston rod.

Provision may be made to exclude dirt or dust from contacting the pistonrod. For example, a flexible boat may be connected between the cylinderand piston rod skid assembly or provision may be made to continuallywash the piston rod.

We claim:

1. An irrigation system comprising an elongate flexible sprayline forconnection at one end to a source of water under pressure, an hydraulictowing device connected to the other end of said sprayline and driven bythe water therein, said sprayline being disposed to trail behind saidtowing device, said towing device comprising a cylinder housing as apiston, said piston having a piston rod which extends from saidcylinder, valve means operable to cause said water under pressure toreciprocate said piston and piston rod relative to said cylinder,supporting means for said piston rod, said towing device including meansfor discharging the water therefrom, said cylinder and said supportingmeans each including a one-way means essentially preventing movement ofsaid cylinder and said piston rods in a rearward direction so that thetowing device will move in a forward direction only, and a tie linehaving means for swivelly securing same to an anchor means in the areato be irrigated and said tie line being secured to said towing device toconstrain it to move in a generally circular path around the area to beirrigated.

2. An irrigation system according to claim 1, wherein said cylinder ismounted on supporting means having said one-way device secured thereto.

3. An irrigation system according to claim 1, further including meanssecured to said piston rod supporting means or to said piston rod andengaging the ground to pull the piston rod in he opposite direction tothe pull of the sprayline thereon to counteract the application oflateral bending moments to said rod by said sprayline.

4. An irrigation system according to claim 1, wherein said valve meanscomprises a valve in said piston, said piston rod being tubular andbeing connected at its free end to said sprayline and having a waterdelivery passage therein opening to said cylinder, said valve havingmeans engaged by the ends ofthe cylinder at the end of each pistonstroke to operate the valve to change the direction of movement of thepiston relative to the cylinder, and a normally open valve at forwardend of the cylinder for controlling the speed of discharge of water fromthe cylinder and thus the rate of movement of the towing device.

5. An irrigation system according to claim 4, wherein said valveincludes a valve body slidably mounted on a stem adapted to engage theends of the cylinder to actuate the valve, a tension spring secured tosaid valve body and to said stem, and a shroud for housing the valvebody in the fully open position, said opening of said valve occurringwhen the force stored in said spring by movement of said stem exceedsthe force of the water on the valve body.

6. An irrigation system according to claim 4, wherein said cylinder andsaid piston rod are supported on skids, said one-way devices including aplurality of trailing legs pivotally secured to said skids adapted todig into the ground to essentially prevent rearward movement of saidskids and which are easily withdrawn on forward movement of said skids.

7. An irrigation system according to claim 4, further including springmeans secured to said valve and said means engaged by the cylinder endsand operable to store energy immediately prior to at least the openingmovement of said valve, said spring means acting to actuate the valvewhen the energy stored in the spring exceeds the force of water on thevalve.

8. An irrigation system according to claim 1 further comprising one ormore similar hydraulic towing devices'connected to said waterlineintermediate said towing device and said source, said towing devicesbeing interconnected by said tie line, said intermediate towing deviceseach having a control valve and actuating means therefore actuated by achange in angular position of said tie line relative to the respectivetowing device to ensure that the towing devices remain substantially inline with each other.

9. An irrigation system according to claim 8, wherein said actuatingmeans comprises an actuator connected to the control valve, a controlwire connected at each end to said tie line and passing over pulleysarranged at either side of the actuator and connected thereto, andspring means biasing the valve actuator in the opening direction.

10. An irrigation system according to claim 8, wherein said actuatingmeans comprises an actuator connected to the control valve, pivotedlevers having secured at one end to the tie line, and a control wiresecured to one lever, passing over a pulley on the other lever, a pulleyon the pivot of said levers and connected to said actuator.

11. An irrigation system according to claim 8, wherein the connection ofsaid sprayline to the intermediate towing devices comprises a flexiblepipe to which the parts of the sprayline are connected extending overthe piston rod and secured thereto and/or to said supporting meanstherefore, a further pipe communicating with said flexible pipe and saidpiston rod to deliver water thereto, said sprayline parts beinguniversally connected to said piston rod or said supporting means.

12. An irrigation system comprising an elongate sprayline for connectionat one end to a source of water under pressure, an hydraulic towingdevice connected to the other end of said sprayline and driven by thewater therein, said towing device comprising a cylinder housing a pistonhaving a piston rod which extends from said cylinder, valve meansoperable to cause said water under pressure to reciprocate said pistonand device moves in a forward direction only, said towing device havinga member secured to said cylinder paral lel thereto for engaging theground to a depth a small distance below the lower most point of saidtowing device to resist lateral forces applied to said cylinder.

1. An irrigation system comprising an elongate flexible sprayline forconnection at one end to a source of water under pressure, an hydraulictowing device connected to the other end of said sprayline and driven bythe water therein, said sprayline being disposed to trail behind saidtowing device, said towing device comprising a cylinder housing as apiston, said piston having a piston rod which extends from saidcylinder, valve means operable to cause said water under pressure toreciprocate said piston and piston rod relative to said cylinder,supporting means for said piston rod, said towing device including meansfor discharging the water therefrom, said cylinder and said supportingmeans each including a one-way means essentially preventing movement ofsaid cylinder and said piston rods in a rearward direction so that thetowing device will move in a forward direction only, and a tie linehaving means for swivelly securing same to an anchor means in the areato be irrigated and said tie line being secured to said towing device toconstrain it to move in a generally circular path around the area to beirrigated.
 2. An irrigation system according to claim 1, wherein saidcylinder is mounted on supporting means having said one-way devicesecured thereto.
 3. An irrigation system according to claim 1, furtherincluding means secured to said piston rod supporting means or to saidpiston rod and engaging the ground to pull the piston rod in he oppositedirection to the pull of the sprayline thereon to counteract theapplication of lateral bending moments to said rod by said sprayline. 4.An irrigation system according to claim 1, wherein said valve meanscomprises a valve in said piston, said piston rod being tubular andbeing connected at its free end to said sprayline and having a waterdelivery passage therein opening to said cylinder, said valve havingmeans engaged by the ends of the cylinder at the end of each pistonstroke to operate the valve to change the direction of movement of thepiston relative to the cylinder, and a normally open valve at forwardend of the cylinder for controlling the speed of discharge of water fromthe cylinder and thus the rate of movement of the towing device.
 5. Anirrigation system according to claim 4, wherein said valve includes avalve body slidably mounted on a stem adapted to engage the ends of thecylinder to actuate the valve, a tension spring secured to said valvebody and to said stem, and a shroud for housing the valve body in thefully open position, said opening of said valve occurring when the forcestored in said spring by movement of said stem exceeds the force of thewater on the valve body.
 6. An irrigation system according to claim 4,wherein said cylinder and said piston rod are supported on skids, saidone-way devices including a plurality of trailing legs pivotally securedto said skids adapted to dig into the ground to essentially preventrearward movement of said skids and which are easily withdrawn onforward movement of said skids.
 7. An irrigation system according toclaim 4, further including spring means secured to said valve and saidmeans engaged by the cylinder ends and operable to store energyimmediately prior to at least the opening movement of said valve, saidspring means acting to actuate the valve when the energy stored in thespring exceeds the force of water on the valve.
 8. An irrigation systemaccording to claim 1 further comprising one or more similar hydraulictowing devices connected to said waterline intermediate said towingdevice and said source, said towing devices being interconnected by saidtie line, said intermediate towing devices each having a control valveand actuating means therefore actuated by a change in angular positionof said tie line relative to the respective towing device to ensure thatthe towing devices remain substantially in line with each other.
 9. Anirrigation system according to claim 8, wherein said actuating meanscomprises an actuator connected to the control valve, a control wireconnected at each end to said tie line and passing over pulleys arrangedat either side of the actuator and connected thereto, and spring meansbiasing the valve actuator in the opening direction.
 10. An irrigationsystem according to claim 8, wherein said actuating means comprises anactuator connected to the control valve, pivoted levers having securedat one end to the tie line, and a control wire secured to one lever,passing over a pulley on the other lever, a pulley on the pivot of saidlevers and connected to said actuator.
 11. An irrigation systemaccording to claim 8, wherein the connection of said sprayline to theintermediate towing devices comprises a flexible pipe to which the partsof the sprayline are connected extending over the piston rod and securedthereto and/or to said supporting means therefore, a further pipecommunicating with said flexible pipe and said piston rod to deliverwater thereto, said sprayline parts being universally connected to saidpiston rod or said supporting means.
 12. An irrigation system comprisingan elongate sprayline for connection at one end to a source of waterunder pressure, an hydraulic towing device connected to the other end ofsaid sprayline and driven by the water therein, said towing devicecomprising a cylinder housing a piston having a piston rod which extendsfrom said cylinder, valve means operable to cause said water underpressure to reciprocate said piston and piston rod relative to saidcylinder supporting means for said piston rod, said towing deviceincluding means for discharging water therefrom, said cylinder andsupporting means each including a one-way means essentially preventingmovement of said cylinder and said piston rod in a rearward direction sothat the towing device moves in a forward direction only, said towingdevice having a member secured to said cylinder parallel thereto forengaging the ground to a depth a small distance below the lower mostpoint of said towing device to resist lateral forces applied to saidcylinder.